The purpose of this project is the study of Aleutian disease of mink (AD), a persistent infection by the Aleutian disease virus (ADV), a nondefective parvovirus. In the past year, we have further compared the infection by ADV in mink and cell culture using Southern blot and dot blot DNA-DNA hybridization analysis. At all levels of infection in cell culture, the predominant form of ADV DNA was the double stranded 4.8 kbp replicative form (RF) monomer, the single stranded virion DNA (SS DNA) was less abundant. In mink tissues, however, RF could be convincingly detected only in spleen and mesenteric lymph node 10 days after infection and the SS DNA was always more abundant than the RF. This suggested that the infection in vivo differs substantially from that in vitro. In addition, 10 day plasma contained large amounts (one billion genomes/ml) of ADV DNA, probably within virions and some of the ADV DNA detected in highly vascular tissues, like liver, may be diluted by plasma virus. These data suggested that at least spleen and mesenteric lymph nodes are true sites of ADV replication.